Ductile cast iron pipes, widely used for water supply and sewer pipes, employ what is known as a push-on type pipe joint structure.
For example, Patent Literature 1 discloses a pipe joint structure having the following configuration. Specifically, into a socket that is formed at an end of one pipe, a spigot that is formed at an end of another pipe is inserted. A sealing rubber ring is disposed in a compressed manner between an inner circumferential surface of the socket and an outer circumferential surface of the spigot. A lock ring provided on an inner circumferential groove portion of the socket engages with a protrusion formed on the spigot, so that the pipe is prevented from being pulled out of the other pipe.
Patent Literature 2 discloses the following configuration. Specifically, whether pipes are assembled with a rubber ring in an appropriate position is determined by measuring a distance between a pipe end of the socket and a position to be in contact with the rubber ring with a feeler gauge, or by inserting a dedicated assembling checker from the pipe end of the socket to the position to be in contact with the rubber ring.